Tape winding mandrel and apparatus

ABSTRACT

A winding mandrel is provided for the simultaneous winding of a plurality of rolls of strip material whereby the tension in each roll is maintained substantially uniform regardless of variations in roll size due to variations in thickness of the strip material.

United States Patent [191 Pennisi et a1.

[ Dec. 10, 1974 TAPE WINDING MANDREL AND APPARATUS Inventors: Joseph V.Pennisi, North Greenbush; Arthur W. Connery, Green Island, both of NY.

US. Cl. 242/56.9, 242/72 B Int. Cl B65h 19/04 Field of Search 242/56.9, 72, 72 B, 68

References Cited 1 UNITED STATES PATENTS 3/1919 Dixon 242/72 B 12/1955 Deichert 242/56.9 X

2,950,071 8/1960 Tidland 242/72 8 X 3,297,270 1/1967 Larson 242/56.9 3,322,361 5/1967 Young 242/56.9

' FOREIGN PATENTS OR APPLICATIONS 1,079,188 8/1967 Great Britain 242/56.9 1,143,074 1/1963 Germany .242/72 B Primary Examiner-John W. Huckert Assistant Examiner-John M. Jillions Attorney, Agent, r Firm-Kenway & Jenney 7] ABSTRACT A winding mandrel is provided for the simultaneous winding of a plurality of rolls of strip material whereby the tension in each roll is maintained substantially uniform regardless of variations in roll size due to variations in thickness of the strip material.

10 Claims, 6 Drawing Figures 24 24 as 39 27 27 29 37 w 33-{r mi 23 i i'::.|

TAPE WINDING MANDREL AND APPARATUS BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates to converting wide rolls of strip material into multiple strips of lesser width and providing such strips in roll form. More particularly; it relates to an apparatus and process of simultaneously winding multiple rolls of strip material under uniform tension.

2. Description Of The Prior Art Various products, e.g., plastic films and foils such as those of, e.g., regenerated cellulose, polyethylene, and polyester, photographic films, and, in particular, pressure-sensitive adhesive tape are manufactured in relatively wide widths and wound into so-called jumbo rolls. Afterwards, the web of, e.g., pressure-sensitive adhesive material is unwound, slit into multiple strips or webs of some lesser desired width, and wound simultaneously in suitable lengths onto individual cores.

The cores are customarily arranged in sideby-side fashion on, e.g., two spaced apart, mandrels whereby some of the lesser width strips of tape are wound into rolls by one mandrel and others by the other mandrel. These mandrels are positively driven and unless driven at a speed whereby an acceptable tension level is maintained, the resulting rolls of tape will be wound either too loosely or too tightly. Either of these conditions results in rolls of tape which may be unacceptable for sale requiring either re-winding of the roll of adhesive tape or discarding as manufacturing waste. Neither is desirable as such actions result in overall increased manufacturing costs.

There are, of course, various slitting and winding procedures known and apparatus available commercially therefor. With one such apparatus, the cores are positively and firmly gripped and winding tension is controlled by controlling the driving force transmitted to the mandrel by a clutch arrangement. The mandrel in such an apparatus slips in the event excessive winding tensions are encountered during winding. Thus, the rolls are wound under some lesser tension.

Even though the winding tension be at an acceptable level, it must also be distributed uniformly among each of the individual strips of reduced width being wound. A corollary to this is that the diameters of the individual rolls being wound must increase at a uniform rate and at any given point in time be equal to each other. Experience in the manufacture of pressure-sensitive adhesive tape has shown, however, that either of these conditions is difficult to attain. It is extremely difficult to attain either condition without use of certain winding procedures and apparatus. l-leretofore, this has involved relatively great expense.

One apparatus heretofore intended to control winding tension in individual rolls of strip material is disclosed in US. Pat. No. 2,855,161. Therein, the rolls on the mandrel are driven through individualclutch devices each comprising two members, one of which is fixed on the mandrel to drive the other which is free to rotate and on which is located the core. Tension, according to-the patentee, is maintained at substantially the same value by applying the same torque to affect the winding of each of the rolls. A more accurate constant driving torque is established by permitting slippage to occur between the driving member of the clutch and the driven member. i

As will be appreciated by those skilled in the manufacture of pressure-sensitive adhesive tapes, the reasons for non-uniform winding, i.e., roll, tension are many. Variations in backing member thickness and weight of adhesive mass, longitudinally as well as laterally of the backing member, result in unequal rates of increase of roll diameters and consequently tension distribution among the winding strips of adhesive material. Even though the variations be slight, the effects thereof, as hereinafter discussed,may be quite pronounced. Thus, rolls where the tape was cut from thin portions of the web of adhesive material will appear loose and sloppy whereas rolls cut from thick portions of the adhesive web may be wound so tightly as to necessitate cutting from the mandrel or cause the cores or removal from the mandrel to collapse or the rolls to become misshapened or telescoped.

As will be understood, where the angular'velocity of the mandrel, hence the cores located thereon is constant, as is the rate of feed of the web of adhesive material at any given point in time to the cores, the variations in thickness of each individual strip of adhesive material brings about variations in roll diameter. These variations result in differences in linear speed for each strip of material being wound. Those rolls having larger diameters will, by merit of their larger circumferences, wind at a higher tension. Thus, the strips being wound in these rolls will be taut. The strips of adhesive material wound on smaller diameter rolls will not be taut. They will be relatively loose.

SUMMARY OF THE INVENTION Our invention overcomes the above-mentioned problems in the provision of a so-called slipping core mandrel in the winding of individual rolls of, e.g., pressure-sensitive adhesive tape. Non-uniform roll tension is eliminated by compensating for unequal thicknesses, both in the machine and cross direction, in either the tape substrate or its applied coating material. This compensation is achieved by imposing a limiting torque condition on each tape core which, if exceeded, will allow the core to rotate with respect to the mandrel (actually the frictional contact with the core permits it to slip on the rotating mandrel) while not affecting its position with respect to the long axis thereof. Core rotation, in a sense, will thus be in a direction opposite to that of mandrel rotation. V

The tape roll cores, rather than being firmly gripped by the mandrel, are permitted to react individually and independently to the tension level in the particular. strip of adhesive material being wound. This reaction, as before indicated, can be said to take the form of core rotation, relative to the mandrel, and in a direction opposite to that of the rotating mandrel. Since the amount of core rotation, i.e., slippage, is directly proportional to the tension level in the adhesive strip being wound, it follows that those rolls tending to have a larger diameter will be wound at a lower net angular velocity than rolls of a smaller diameter. Moreover, since the frictional, or driving force, between the mandrels and the cores is essentially uniform among the cores and independent of the relative angular velocity between the mandrel and the cores, it also follows that the tension level in the strips of adhesive tape being wound will at any given point in time, be uniform.

Finally, with a constant frictional, or driving force, between the mandrel and the cores, it may be reasoned that rolls wound with this invention will exhibit a constant torque winding pattern. However, an essentially constant tension winding pattern may be generated by programming this driving force as some function of the instantaneous winding roll diameter.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood by referring to the drawing in which like numerals refer to like parts in the various views and in which:

FIG. 1 is a schematic illustration of apparatus for slit ting a web material into a plurality of more narrow strips and winding the strips simultaneously into rolls;

FIG. 2 is a top view showing the narrow strips in FIG. 1 being wound into individual rolls on a common mandrel;

FIG. 3 is a more detailed side view, partly in section, of the winding mandrel of our invention;

FIG. 4 is an end view of the mandrel shown in FIG. 3, looking from the right end, the end plate being removed;

FIG. 5 is an end view of one of the core engaging members of the mandrel shown in FIG. 3 but removed from the mandrel; and

FIG. 6 is a side view of the core engaging member of FIG. 5.

DETAILED DESCRIPTION AND SPECIFIC EMBODIMENT OF THE INVENTION Turning now to the drawing, there is disclosed, in diagrammatic fashion, in FIG. 1, a sheet or web 10 of pressuresensitive adhesive material being unwound from a supply roll 11 thereof. The supply roll, or as such a roll is sometimes called, the bundle roll, is supported in conventional fashion for rotation on a mandrel or unwind shaft 12, such roll being rotatable in the desired width by a gang of circular knives 18 spaced axially and parallel to the axis of roll 16. The knives are urged against the traveling web 10 and roll 16 by means well-known in the art, roll 16 acting somewhat as an anvil for the circular cutting knives.

After the slitting operation, strips 17a, 17b of pressure-sensitive adhesive tape pass, every other one, to rewind mandrels 19a, 1%, respectively. Thereon, the strips of tape are wound individually and simultaneously onto cores (not shown) spaced axially along the respective mandrels.

The cores, well known to those in the pressuresensitive adhesive tape art, may be of various materials. However, in general, the coresv are of heavy paper and are cut to the desired width from cylindrical tubes thereof. The tubes are formed of the desired diameter by helically winding the desired paper and adhesively securing the convolutions so formed.

Mandrels 19a, 19b, which are identical in design, are mounted for rotation, in the direction indicated by the arrows, and can be, as is usual, removed from the slitting and rewind apparatus to facilitate loading thereof with the desired number of cores. Such a feature is conventional in the slitting and rewinding of pressuresensitive adhesive material and is believed to require no detailed explanation herein. The mandrel, in general, is, loaded with cores by means of a so-called core box which provides that the cores are spaced axially, as desired, along the mandrel for winding the slit strips 17a, 17b of adhesive material.

Mandrel 19a, which, as before-mentioned, is identical to mandrel 19b, is of generally cylindrical shape,as shown more clearly in FIG. 4 of the drawing. Each mandrel comprises an elongated tubular shaped mandrel body member 20 which, in cross-section, is of incomplete circular shape formed by an are as shown. Mandrel body 20 has located. inwardly thereof and along its length a compartment 21. This compartment in the preferred instance including a diaphragm or rubber bladderchamber 22. A rubber bladder, not-shown contained in chamber 22, on being inflated engages with and exerts an outward force on a plurality of spring loaded bolts 23 disposed axially along body member 20 each being connected to an arcuate shaped core engaging member 24. These bolts, in turn, being connected to the arcuate shaped core engaging members 24, cause the members to engage the cores associated therewith. Thus, as will be seen hereinafter, outer peripheral surface 25 of arcuate member 24 engages the inner periphery of the circular shaped core whereby the cores may be frictionally gripped individually under some desired force.

The force which the arcuate member exerts on the core is, as will be obvious, a function of the bladder pressure and is subject to control by usual means via air valve designated by reference numeral 26- (FIG. 3). Thus, a limiting torque may be generated at the arcuate member-core interface which is a function of the bladder pressure, surface area of the bolts 23 in contact with the bladder, surface area'of the arcuate member in contact with the core, surface area of the mandrel body in contact with the core, and the frictional characteristics of the latter two interfaces. Assuming that all of these conditions, excluding bladder pressure, to be essentially constant, it thus follows that the limiting torque value is also a function of the bladder pressure. Thus, it is obvious that a constant bladder pressure will provide a constant torque winding pattern and that a constant tension winding pattern can be achieved by continuously increasing the bladder pressure as some function of the instantaneous winding roll'diameter.

Arcuate, core engaging members 24 are, as seen more clearly in FIG. 6, provided with a core engaging surface 25 which, in general, corresponds to and is only slightly of greater width than the core associated therewith. Shoulders 27, also of arcuate shape, are provided on each side of core engaging surface 25. The width of these members may, for example, be about'half that of the core width; however, there is no reason why this dimension cannot be whatever desired. Shoulders 27, as shown clearly in FIGS. 5, 6 extend outwardly a greater radial distance than does core engaging surface 25. In

this way, the core associated with arcuate surface 25 will be prevented from axial movement and its direction of movement will be substantially rotational. Al-

though the radial difference in dimension can be varied somewhat, a suitable difference is that slightly less than core thickness.

An alternative to raised shoulders is to provide shoulders 27 of the same radial dimension as core engaging surface 25 but of different frictional characteristics. For example, coating the shoulders with material of high frictional characteristics will prevent lateral displacement of the core.

Each core engaging member 24, as seen in FIGS. 4 and 5, has, at each extremity of arcuate surface 25, bearing surfaces, which'in the preferred instance, are provided by stepped milled vertical faces 28 and horizontal resting surfaces 29, the use for which will be later explained, if not already obvious. The base or bottom surface 30 of arcuate core engaging member 24 is of planar shape and is parallel with horizontal resting surfaces 29. As is obvious from FIG. 5, the bearing surfaces interconnect the base surface 30 and arcuate core engaging surface 25. A threaded hole 31 is provided in each core engaging member for a spring loaded bolt 23.

Arcuate core engaging members 24, as may mandrel be of various materials, e.g., hard, rigid plastics such as polyacetal resins and metals such asstainless steel, aluminum, magnesium, etc.. They may be of the same or different material, e.g., arcuate members 24 may be of aluminum and mandrel body 20 of magnesium, extruded or otherwise formed into the desired shape. The latter material is found particularly satisfactory for the mandrel body where the mandrel must be man-handled in removing it from the slitting and wind-up apparatus. Regardless ofwhat materials of construction are used, they must be, in general, of sufficient hardness to resist abrasion by the cores inner periphery. In some cases, it may be found desirable to provide core engaging surfaces 25 with a surface of more suitable wearing and frictional characteristics. This surface may be, for example, chrome plated or providedwith a coating of TEFLON polytetrafluorethylene.

Mandrel' body 20, as shown in FIG. 3, is provided with end plates 32 which are removably attached to the body by means of conventional screw fastening means 33. Shaft studs 34, which may be of circular crosssection or otherwise, as desired, are provided integrally with end plates 32 for mounting the mandrel for rotation. A slotted elongated planar shaped plate 35 is provided within compartment 21 for axial location of arcuate core engaging segments 24. This plate, moreover being parallel to base surface 30 of the arcuate segment or core engaging member provides a support surface for the base surface when the core engaging members are in their retracted position. The plate may be fastened to mandrel body 20 by various means (not shown) such as, e.g'., screw fastening means, epoxy resin adhesive, etc.. Alternatively, it may be secured in the desired position by engagement of the ends thereof in slots in end plates 32.

As will be appreciated, while only three core engaging segments 24 are shown in the drawing, this number will, of course, depend on the mandrel used and the width of the adhesive material being slit and wound into narrow roll material. Arcuate segments 24 are attached to slottedplate 35 by means of spring loaded bolts 23, the spring being denoted by reference numeral 36. Thus, a positive force is provided for retraction of the arcuate segment once the bladder no longer exerts a force or screw threaded bolt 23.

Alternatively, the arcuate core engaging segments 24 can be associated with the mandrel body in other ways. One such means is to replace slotted plate 35 with an alignment bar having holes therein of proper dimension to accommodate a spring loaded shaft attached by screw means to the core engaging segment. As will be appreciated, each hole will contain a bushing of suitable material to provide the desired bearing surface for outward movement and to prevent lateral displacement of the arcuate member.

The arcuate core engaging members 24, as shown in FIG. 3, in the preferred embodiment are aligned axially on mandrel body 20 by alignment bolts 37. These bolts are screw threaded as shown, being provided in end plates 32 in screw threaded holes 38. On the inner end of the alignment bolts are located bearing plates 39 for contact with and movement of the associated arcuate segments. In turn, the other segments may be moved, as desired.

As an alternative to spring loaded bolt 23, a short rod or shaft, circular or otherwise, may be used. This may necessitate use of a spring retainer. However, these are known in the art. More than one bolt or shaft may be found desirable to prevent undesirable rotational displacement once the bladder is pressurized and the arcuate segment is moved radially outwardly to engage the core inner periphery.

In the non-operating position, e.g., before the bladder ispressurized, arcuate segments 24 are substantially in contact with mandrel body 20 and, in combination therewith, completes the cylindrical crosssectional shape. Resting or bearing surfaces 29 are supported by horizontal support surfaces 40 located on and integral with and forming a partof mandrel body 20. As shown in FIG. 4 support surfaces 40 being located along the length of body member 20 are opposite the bearing surfaces on arcuate segments 24. These support surfaces mate with bearing or horizontal resting surfaces 29, the support surfaces being parallel with bottom surface 30 and slotted plate 35. In the nonoperating or retracted position, as shown in FIG. 4, Le.

when the bladder is not pressurized, opposed bearingcore associated therewith. Although the are defined by the core engaging surface may be varied as desired, a suitable arcuate surface will be provided where the arc is about 50, the segment having been machined, e.g., from an aluminum bar stock having a 3 inch diameter.

Operationally, a'mandrel is first provided with the desired number of core engaging segments depending on the width of adhesive web to be slit and the width of each slit strip of adhesive material. The mandrel is positioned in a suitable core box and the cores are engaged with the respective arcuate core engaging surface. This is accomplished when the air valve is opened and the apparatus and the slitting and winding operation begun as usual at some suitable speed. Tension in the various strips is then controlled by the limiting torque value imposed on the cores and the instantaneous diameter of the rolls being wound.

During winding, as the diameter of the rolls build up, those rolls increasing in diameter most rapidly will be found to cease rotating in the direction of the mandrel rotation and the cores thereon will slip. Thus, the winding tension on these rolls will be more or less stabilized and maintained at the same level as that in other rolls of lesser diameter at that point in time. As the diameter of other rolls increases more rapidly than the remaining rolls, their cores in turn will be caused to slip on the mandrel.

On attaining the desired length of material on the roll cores, winding is stopped in the usual manner, the strips are cut, and the mandrel is removed from the apparatus. The bladder is then vacuated thereby allowing the arcuate core engaging segments to retract. The rolls of tape are then easily removed from-the mandrel.

To demonstrate the performance advantages of the slipping core mandrel of this invention in the manufacture of pressure-sensitive adhesive tapes, as compared to a mandrel conventionally used not allowing for core slipping, a pressure-sensitive adhesive material was manufactured wherein a non-uniform coating weight was purposely generated. This was accomplished by coating a 2] inch wide sheet of cellophane (regenerated cellulose), which had been previously primed and backsized, according to usual materials and techniques, with a non-uniform weight of a conventional rubberbased adhesive composition.

The adhesive composition was applied using a threeroll reverse roll coater and the non-uniformity was generated by skewing the metering roll gap from .006 inches on one side to .01 1 inches on the other. This variation resulted in a measured adhesive mass weight range of from about 0.75 oz./yd. to about 1.05 oz.- /yd. Assuming a linear distribution within this range, the weight in the center of the web of adhesive material is therefore approximately 0.90 oz./yd.

The" roll bundle thus produced was then reduced to two rolls, each 10% inches wide. This provided two supply rolls of non-uniform weight, one having an adhesive mass ranging from about 0.75 oz./yd. to about 0.9 oz./yd. the other having an adhesive mass ranging from about 0.9 z./yd. to about 1.05 oz./yd. The latter roll was selected for the remainder of the experiment.

Two successive cuts were made of the supply roll of adhesive material thereby providing adhesive strips one inch wide by 72 yds. long. This was accomplished according to usual techniques using a full width tape slitter. Thus, a total of nine rolls of adhesive tape were obtained from each cut. Five of these rolls were wound on cores on a conventional winding mandrel providing positive gripping, i.e., not allowing for core slippage. These were identified by reference numerals 1, 3, 5, 7, and 9. The remaining four rolls of tape were wound on x the slipping core mandrel of this invention operating at the same imput rotational speed as the other mandrel and these rolls were identified by numbering them 2, 4, 6, and 8.

The rollsof' tap'e" we're rammed frornihe' mandrels and after the usual visual inspection were subjected to hardness testing. Hardness of a roll of pressuresensitive adhesive tape is a quantitiative measure, ex-

, pressed in mils, of the tightness of wind of the individ-- ual tape layers which comprise the roll. This measurement is made through theuse of an instrument called a Roll Hardness Tester.

. The Roll Hardness Tester consists essentiW of a one-quarter inch diameter steel ball attached to the end of a spring loaded spindle, an 800 gram weight, a vertically adjustable mechanism to support the tape roll under evaluation, and a dial indicator calibrated in mils. In use, the roll of tape to be tested is placed in the support mechanism in a vertical plane, i.e., roll sidewalls are perpendicular to the ground plane, and its position is adjusted vertically to contact and raise the A inch diameter steel ball to obtain an initial dial reading of lOO mils. The point of contact between the steel ball and the tape roll is on a line which passes through the center of the roll face and is perpendicular to the ground plane. The roll of tape is secured in this position and the indicator spindle is placed under an 800 gram static load. This load causes the ball to depress the' outer layers of the tape roll by an amount which is an inverse function of the tightness of wind. Aftera 10 second dwell, under load, the indicator reading is observed and the roll hardness value is determined by subtracting this reading from the initial indicator reading of one hundred. The results for the rolls aboveindicated are tabulated below.

Unsaleable Slipping Standard Core Mandrel Mandrel Roll No. Hardness Roll No. Hardness Remarks Condition Cut No. 2

l 44 Fluted & Gapped Unsaleable 2 8 OK Saleable 3 36 Fluted & Gapped Unsaleable 4 8 OK Saleable 5 14 Fluted Unsaleable 6 12 OK Saleable 7 8 OK Saleable 8 10 OK Saleable 9 8 Unsaleable Crushed Core inspection of the above data clearly indicates the in sensitivity of the slipping core mandrel to variations in adhesive weight across the supply web of adhesive material, and the extent to which rolls wound on a nonslipping core mandrel are affected by this same condition. Similar good results will be forthcoming with our invention whether nonuniformity in web thickness is due to variations in coating weights, substrate thickness, or a combination of these factors.

While our invention has been described more particularly with respect to pressure-sensitive adhesive tape, those skilled in the art of winding will readily appreciate that it is not so limited. The invention may find application wherever progressive winding of strip-like material on adjacent cores on a common mandrel occurs. The mandrel of this invention will be found suit-' able in various slittingand winding apparatuses now used. Moreover, many different embodiments of the invention will obviously appear to those skilled in the art, it being understood that the specific embodiments of the invenTion, as disclosed above, are intended by way of illustration only and not limiting on the invention, but that the limitations thereon are to be determined only from the appended claims.

What we claim is:

l. Mandrel of generally cylindrical shape for the simultaneous winding of a plurality of rolls of strip material onto individual cores spaced axially along the mandrel whereby the tension in each roll is maintained substantially uniform, said mandrel comprising:

a. an elongated tubular shaped body member being in cross-section in the shape of an incomplete circle formed by an arc, a compartment located inwardly hereof, and a support surface at each end of the are along the length of the body member and integral therewith; r b, a plurality of core engaging members located axially along and in operative engagement with said 1 body member, each said core engaging member having a base surface of planar shape and an arcuate shaped core engaging surface, and having bearing surfaces interconnecting said base surface and said arcuate shaped core engaging surface, each said core engaging member being individually mounted for movement radially outwardly from and into retractable engagement with said body member, said core engaging members on said outward movement each engaging the inner peripheral surface of an associated core whereby each core is frictionally gripped by the core engaging member 5 with some desired force; the bearing surfaces on each said core engaging member in itsretracted location contacting the opposed support surface on 7555533 r'iienisermers esn iain nacireuar cross-section and cylindrical shape of the mandrel;

c. an elongated planar shaped member located in the inwardly located compartment of said body member and connected to said body member, said elongated member being associated with each said core engaging member and providing a support for the base surfaces thereof;

d. means associated with the said elongated member and with the base surface of the core engaging members providing a positive force for retraction of each said core engaging member and whereby each said core engaging member will retract and the base surface thereof will be supported on said elongated member; and

. means located within said mandrel body member and in said compartment associated with said first named means for exerting an outward force on each said core engaging member.

2. Mandrel according to claim 1 wherein the core engaging members include arcuate shaped shoulders and the arcuate shaped core engaging surface of each said arcuate shaped member is intermediate said arcuate shaped shoulders, said shoulders limiting axial displacement of the core engaged by each said member and permitting the movement thereof to be substantially rotational.

3. Mandrel according to claim 1 in which the support 7. Mandrel according to claim 1 wherein said second named means comprises an inflatable bladder whereby on inflation said core engaging members are urged radially outwardly for engagement with each respective core.

8. Mandrel according to claim 1 wherein the first named means comprises a spring loaded member;

9. Mandrel according to claim 1 wherein the arcuate shaped surface describes an arc of about 50.

10. Mandrel according to claim 1 wherein the arcuate surface is chrome plated. 

1. Mandrel of generally cylindrical shape for the simultaneous winding of a plurality of rolls of strip material onto individual cores spaced axially along the mandrel whereby the tension in each roll is maintained substantially uniform, said mandrel comprising: a. an elongated tubular shaped body member being in crosssection in the shape of an incomplete circle formed by an arc, a compartment located inwardly hereof, and a support surface at each end of the arc along the length of the body member and integral therewith; b. a plurality of core engaging members located axially along and in operative engagement with said body member, each said core engaging member having a base surface of planar shape and an arcuate shaped core engaging surface, and having bearing surfaces interconnecting said base surface and said arcuate shaped core engaging surface, each said core engaging member being individually mounted for movement radially outwardly from and into retractable engagement with said body member, said core engaging members on said outward movement each engaging the inner peripheral surface of an associated core whereby each core is frictionally gripped by the core engaging member with some desired force; the bearing surfaces on each said core engaging member in its retracted location contacting the opposed support surface on the body member thereby completing the circular cross-section and cylindrical shape of the mandrel; c. an elongated planar shaped member located in the inwardly located compartment of said body member and connected to said body member, said elongated member being associated with each said core engaging member and providing a support for the base surfaces thereof; d. means associated with the said elongated member and with the base surface of the core engaging members providing a positive force for retraction of each said core engaging member and whereby each said core engaging member will retract and the base surface thereof will be supported on said elongated member; and e. means located within said mandrel body member and in said compartment associated with said first named means for exerting an outward force on each said core engaging member.
 2. Mandrel according to claim 1 wherein the core engaging members include arcuate shaped shoulders and the arcuate shaped core engaging surface of each said arcuate shaped member is intermediate said arcuate shaped shoulders, said shoulders limiting axial displacement of the core engaged by each said member and permitting the movement thereof to be substantially rotational.
 3. Mandrel according to claim 1 in which the support surfaces on the body member are parallel to the elongated planar shaped body member and the base surfaces on the core engaging members.
 4. Mandrel according to claim 2 wherein said shoulders extend outwardly a greater radial distance than said core engaging surface.
 5. Mandrel according to claim 4 wherein said radial distance difference is slightly less than the thickness of the core.
 6. Mandrel according to claim 2 wherein the width of said core engaging surface is only slightly greater than the width of the associated core.
 7. Mandrel according to claim 1 wherein said second named means comprises an inflatable bladder whereby on inflation said core engaging members are urged radially outwardly for engagement with each respective core.
 8. Mandrel according to claim 1 wherein the first named means comprises a spring loaded member.
 9. Mandrel according to claim 1 wherein the arcuate shaped surface describes an arc of about 50*.
 10. Mandrel according to claim 1 wherein the arcuate surface is chrome plated. 